The military had more than four hours' warning of the raid by Boko Haram militants, BBC quoted the human rights group as saying Friday citing credible sources.

Fifty-three of the girls escaped soon after being seized in Chibok April 14 while over 200 remained captive.

According to the Amnesty International, one reason was a "reported fear of engaging with the often better-equipped armed groups".

Amesty's Africa Director Netsanet Belay said it amounted to a "gross dereliction of Nigeria's duty to protect civilians".

Meanwhile, Nigeria's authorities, "doubt the veracity" of the Amnesty report. "If the government was aware (beforehand) there would have been an intervention (against the militants)," Nigerian Information Minister Labaran Maku said, adding the authorities would still investigate the claims.

During a meeting of the World Economic Forum in Abuja, Nigerian President Goodluck Jonathan Friday told journalists that he believed the schoolgirls were still in the country and had not been shifted to neighbouring Cameroon.

A father of one of two of the missing schoolgirls said he believed there was "politics" behind the kidnappings because there was prior information that the militants would be coming to Chibok.

Boko Haram has admitted capturing the girls, saying they should not have been in school and should get married instead. In a video released earlier this week, leader Abubakar Shekau threatened to "sell" the students.

Teams of experts from the US and Britain -- including military advisers, negotiators and counsellors -- have arrived in Nigeria to help locate and rescue the abductees.